php简略注册代码求帮忙

    //Author:avirtuous
    $con = mysql_connect("localhost","root"," ") or die('Cloud not connect:'.mysql_error());
    mysql_select_db("demo",$con);
    $un = $_POST['username'];
    $pwd = $_POST['password'];
    $result=mysql_query("INSERT INTO user (username,password) VALUES ($un,$pwd)");
    if($result){
        echo "注册成功";
    } else {
        echo "注册失败";
    }
?>

015-03-11 00:00:04 19492 [Note] Server socket created on IP: '::'.
2015-03-11 00:00:05 19492 [Note] Event Scheduler: Loaded 0 events
2015-03-11 00:00:05 19492 [Note] wampmysqld: ready for connections.
Version: '5.6.12-log'  socket: ''  port: 3306  MySQL Community Server (GPL)

[Wed Mar 11 14:50:59.548409 2015] [:error] [pid 6216:tid 1696] [client ::1:13262] PHP Stack trace:, referer: http://localhost/zc.html
[Wed Mar 11 14:50:59.549479 2015] [:error] [pid 6216:tid 1696] [client ::1:13262] PHP   1. {main}() E:\\wamp\\www\\reg.php:0, referer: http://localhost/zc.html
[Wed Mar 11 14:50:59.549479 2015] [:error] [pid 6216:tid 1696] [client ::1:13262] PHP   2. mysql_connect() E:\\wamp\\www\\reg.php:3, referer: http://localhost/zc.html